Method of heating steel slugs for forging or extrusion



Dec. 7, 1954 A. F. KRlTscHER 2,696,373

ME'rHoD OF HEATING STEEL sLUGs FOR FORGING OR zEx'rRUsIoN l Filed Aug.13 1951 FIE United States Patent" O METI-IOD OF HEATING'STEELSLUGS FORFORGING OR EXTRUSION Application August 13,. 19511, .Serial No. 241,6197 Claims. (Cl. 263-62) This invention relates to the heating of massesof metal and, in particular, to the heatingV of billets ,or slu'gs* ofsteel for hot-working by extrusion or' forging.

The extrusion of steel through formin'g'dies accomplished but requires aspecial technique andis still beset with numerous difficul'ties. Forexample, the heating of the billets or Slugs has usually been eifectedin conventional furnaces at relatively low rates. `The heavy Scaleresulting is abrasive in Character and causes rapid wear of the dies,besides reducing the product yield per pound' of billet weight. Suchscale is not fully removed by conventional descaling practice and' theport-ion left' on the billets impairs' the surface' finish'k of theextruded product, In addfhas been besides damagin'g the d'ies. tion, thepower required for the extrusion operation has been very high.Experience has shown, furthermore, that stainless-steel;,billets heatedby conventi'onalf; methods and equipment, i. e., involving long heatingtimes suchas several hours, occasionally willl not "push" when' placedin the press, al'though heated to the proper temperature.

' I have inventeda novel method of heating steel. billets or' slugs forextrusionwhichV overcomes these difficulties and is characteri'zed byfurther important advantages. The invention is also useful in' heatingbillets for ordinary forgi-ng Operations. My invention. is based on'thefact that ordinary steel, while losing most of its* tensile strength attemperatures in 'the n'eighborhood. of those required for forging orextrusion', still retains sufficient strength at such te'mperat'uresVto' sustain substantial loads. Recent investigations show, for example,that low-carbon steel'has a short-time tensile strengt of about. 2500 p.s. i. at 2000 F. and about l5001p'. s`. i. at 2`3'00' F'. I takeadvantage of this fact to provide a novel method of supporting andhandling billets or Slugs while .being heated for working by forgingor'extr'us'i'on. I' 'also u-tilize an irnproved type of 'heating' furnace.andneifect the heating at a rate much greater than has beerr thoughtpossible heretofore. I am thereby enabled to utilize fully theshort-time strength at high temperatures.

In a preferred practice, I weld a steel Stud to one end of a billet orslug and, by means of the welded-on Stud, I support the slug whileconveying it through a continuous, panel-type furnace which heats itrapidly to extrusion or forging temperature. After the billet has beenheated and while still suspended by the Stud, I subject it on emergingfrom the furnace to a descaling treatment and also immerse it in a fusedSalt bath heated to about the desired final temperature of the billet.After a short time, I remove the billet from the bath, shear off thestud and then deliver the billet immediately to the extrusion press.

A complete understanding of the invention may be obtained from thefollowing detailed description and explanation which refer to theaccompanying drawings ill ustrating the present preferred practice. Inthe drawmgs,

Figure 1 is a diagrammatic elevation illustrating the welding of a Studto one end of a billet;

Figure 2 is an elevation partly broken away showing the heating furnacewith a billet traveling therethrough;

Figure 3 is a partial cross-section through the furnace;

Figure 4 is a Vertical section through a water-spray descaler;

Figure 5 is a longitudinal Vertical section through the salt-bathcontainer;

Figure 6 is a diagram the stud;

illustrating the shearing oif of 2,6%,378 Patented Dec. 7, 1954 ICCVFigure. 7 is an-el'evatio'n of ltheupper end of the billet showing thehook for suspending it and the Shield for protectin'g theV supportingStud; and I Figure S is a set of curves showing ther progress of theheating of both stainless and low-carbon steel' billetsv by my'invention.

Referring now in detail to the draw-mgs, a billet or sliuig 10- of thedesired composition and having the size and' Shape appropriate for theintended extrusion, has a stud 11 of low-carbon steel flaslr-welded. toone end thereoIf normal to thesurface thereof as shown in Figure 1. TheZbillet will usually be a cylinder several inches in diameter having alength twoor three times the diameter and weighing several. hundredpounds. The Stud is preferably headed and its shank has such diameter asto. provide a section sufficient to carry the billet suspended therebywithout substantial elongation when heated to the maximum billettemperature required for extrusion.

The stud .Welding may conveniently be effected by a conventional device12 designed for such purpose and available` commercially. This deviceoperates first to strike an electric arc between the stud and-billet andthen, after fusing a pool of metal in the surface of the latter, tothrust the Stud forcibly thereinto and hold it there until the' moltenmetal solidifies. Such a weld, When cold,`has a; strength greater thanthat of the` Stud proper. Even at elevat'ed temperatur-es, say 2.300`L`F., the weld Strength is a-pp'roximately equal to that of the Stud.V Aplurality of studs may be used, depending on the weight to be SupportedSince the latter determines the total sectional area of studs' neededfor a given billet.

' When the stud has been welde'd to the billet, the latter is hungon asupporting-hook 13 depending from a conveyor trolley (not shown). Thehook is slotted or bifur- -catedto receive the sha'nk of the stud andengage the undersid'e' of its'l head. The trolley from which the hookdep'endsr travels above a furnace 14' of the panel type having. alongitu'dinal slot in the top thereof through which the shank of thehook passes. The billet is thus quickliy heated' by burners 15 mountedinthe spaced side walls or panelsof the. furnace, as it travels along thelength thereof. `While only one billet is shown in the furnace, it willusually be preferable to pass a continuous succession of billetstherethrough in close order.

Instead of a headed Stud and a bifurcated hook, I may use headless studsand engage them with gripping j'aws carried by a travelingtrol-ley.

Thefiringv rate of the burners, the speed of travel of thebillets andthe length of the furnace are correlated so that the billets are rapidlyheated to a temperature of-about 2300`o VF. The total heating timeshould be .not more than about six minutes per inch of diameter of thebillet and is preferably less, i. e., from three to five minutes perinch of diameter. By reason of the rapid heating, the studs which Willcarry the load stated for thirty minutes, may be relied on to suspendthe billets safely. The heating of the billets according to theinvention is shown graphically in Figure 8 for both stainless steel andcarbon steel. As there shown, the latter heats more rapidly at firstbut, because of the dip in the curve, is soon overtaken by thestainless-steel billet. In both cases, the heating curve is steep andsmoot The heating rate shown far exceeds the maximum rate heretoforethought feasible for stainless steel. An important result of the rapidheating is that only a thin layer of Scale is formed on the billets,which is light and flaky in Character. Such Scale can be easily andthoroughly removed thus saving die wear and insuring a good surface onthe finished product.

In order to reduce the loss of strength by the stud supporting thebillet as they are both heated during travel through the furnace, I mayemploy a cylindrical shield 16 of thermal insulation surrounding theStud and resting on the top of the billet, as shown in Figure 7. Such ashield utilizes the so-called Stack effect." That is to say, the ascentof hot gases through the central region of the Shield will induce adownfiow of cool air along the inner surface of the wall thereof, whichkeeps the stud at a temperature somewhat lower than that of the billet.In addition, the Shield serves as a radiation barrier and the weld as aconduction barrier. The combined effect is aided by the 'za a coolingeffect of the hook which keeps the stud several hundred degrees belowthe temperature of the billet.-

The billets may be rotated as they pass through the furnace, if desired,as by rotating the hooks on which they are suspended, for greateruniformity of heating.

On reaching the exit end of the furnace after being heated to a forgingtemperature of from 1950 to 2300 F., the billets are subjected to adescaling operation as by being lowered into a tank 17 fitted with aplurality of nozzles 18 discharging water sprays at high Velocity.Because of the light, flaky Character of the scale resulting from therapid heating of the billets, it is etfectively dislodged by such spraysso quicldy that no substantial cooling of the billet occurs.

The heated billets are next immersed in an elongated tank 19 containinga bath of fused salt such as barium Chloride, heated to a temperatureapproximating the desired final temperature of the billets, and causedto travel therethrough, thus continuing the immersion for a short time.The salt bath serves several purposes. first place, it exerts adescaling action so that the descaling by water sprays may be omitted ifdesired. The salt bath also equalizes the temperature in variousportions of the billet. Finally it forms a film on the surface of thebillet which acts as a lubricant during the extrusion. O

On reaching the exit end of tank 19, the billet is raised therefrom, andsuspended over the charging chute 20 leading to the inlet to theextrusion press. Then the stud 11 is cut off by shears 21. The billet isthus immediately delivered to the extrusion press for hot workingtherein.

It is to be noted that the invention is characterized by numerousadvantages some of which have already been mentioned. Outstanding amongthese is the reduction in the power required by the extrusion press forworking billets heated according to the invention. In fact, theextrusion ratio of a given press may thereby be increased by as much as10 or 15%. Rapid heating is facilitated by the method of supporting thebillets on a suspending stud and by the use of a panel-type furnace. Thethin scale formed during the quick heating is easily removable and sopermits avoidance of the destructive effect thereof on the forming dies.In additon, the yield of product per billet is increased by reducing theamount of scale. By using a suitable conveyor, the billets may beconveyed through the furnace, descaler and salt bath withoutdisengagement from the supporting hooks 13, thus expediting the overallheating cycle and eliminating conveying baskets or carriers which arevery expensive and have but a linlited life.

Although I have disclosed herein the preferred embodiment of myinvention, I intend to cover as Well any change or modification thereinwhich may be made without departing from the spirit and scope of theinvention.

I claim:

1. In a method of heating billets to temperatures suitable forextrusion,

forging or the like, the steps including In the weld providing a billethaving a metal suspending attachment ed to one end thereof, engaging theattachment with a traveling support to suspend the billet, then passingthe suspended billet and at least a portion of the attachment through anelongated heating chamber, thereby subjecting substantially the entiresurface of the suspended billet uniformly to the heat of the chamber andheating the billet at a rate such that it reaches a forging temperatureexceeding 2000 F. before the strength of the attachment falls below theweight of the billet.

2. The method defined by claim 1 characterized by shearing saidattachment while the billet remains suspended from said support anddelivering the billet by gravity to hot-working means.

3. The method defined by claim 1 characterized by said attachment havinga head and said support engaging the under side thereof.

4. The method defined by claim 1 characterized by supplying heat to thebillet as it traverses the chamber at a rate such as to heat the billetto forging temperature in a time of from three to five minutes per inchof transverse dimension.

5. The method defined by claim 1 characterized by shielding theattachment throughout its entire length while the billet is passingthrough the chamber.

6. The method defined by claim 1 characterized by descaling the billetas it emerges from the heating chamber and then immersing the billet ina bath of fused salt heated to about the same temperature as the billet.

7. The method defined by claim 1 characterized by subjecting the heatedbillet to a water-spray descaling as it emerges from the heatingchamber.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREF ERENCES "High Speed Heating of Steel by Mawhinney in IndustrialHeating, January 1951, vol. XVIII, No. 1, pages 40-44, inclusive.

